In storing food in the household, the primary concern is maintaining freshness of the food. To maintain freshness, two main methods have been employed. The first is refrigeration, and the second is containment. These are typically, but not necessarily, used together for maximum effectiveness. More recently, ethylene gas absorbing compounds have been employed to control ripening of produce.
Refrigeration is the provision of a reduced temperature environment. This reduced temperature environment reduces the grown rate of bacteria and other organisms, slowing their degradation of stored food in a well known manner.
Containment of food in an effort to maintain freshness typically involves sealing the food against air exchange with the ambient environment, preferably at a pressure below atmospheric pressure. This has been achieved in numerous ways, such as by encasement within carefully folded aluminum foil, encasement within plastic bags which may be sealed and possibly evacuated, or placement within a plastic container having an air-tight seal and possibly evacuating air from within the container. Examples of such containment systems include U.S. Pat. Nos. 4,660,355, 4,756,422 and 4,941,310, the assignee of these patents being the assignee of the present patent.
While these storage methods work well for certain foods, it has been found that they are not the best storage method for all produce. Specifically, sealed container storage methods are not best for fresh produce which continues to live for some time after harvest. Since certain produce continues to live after harvest, the produce continues to respirate and produce other gases, including ethylene. Further, the trauma induced by harvest can cause the respiration rate of the produce to increase, sometimes dramatically, over the normal respiration rate of produce in the field. Relatively prolonged exposure to an excessive concentration of the respiration byproducts, particularly ethylene gas, can degrade the appearance, flavor, texture, and other aspects of the produce.
Sealing produce against air exchange, as described above, may simply trap the respiration gasses with the produce and unless the seal is periodically broken to permit air exchange, buildup of an excessive concentration will occur, accelerating the degradation of the produce. Additionally, due to loss of moisture by the produce and ambient moisture in the air, condensation readily can occur inside sealed containers. To prevent this, several containers for produce have provided for gas exchange.
A first example is shown in U.S. Pat. No. 4,676,371 to Byrne. Byrne describes a produce storage container formed of an air-impervious material, but having several gas exchange openings. The openings are formed in a base of the container, and a lid is provided to close the top of this base. A second example is a product sold by TEFAL S. A. under the model name “la legumiere”. This product includes a base formed of an air impervious material, and having a lid. The lid is also formed of an air impervious material, but includes a pair of apertures extending therethrough and a sliding gate which may be manually moved to selectively block one of these apertures. The aperture may not be closed in a gas-tight manner, but does include a filter to prevent ingress of contaminants. Both of these containers may be used within a household refrigerator to increase the freshness of the produce through refrigeration.
To prevent degradation of produce due to exposure to ethylene gas, ethylene gas absorbers have been developed. Such ethylene gas absorbers, as described in U.S. Pat. No. 5,278,112 to Klatte, the full text of which is hereby incorporated herein by reference, describe the use of potassium permanganate impregnated Zeolite crystals to absorb ethylene gas. However, this chemical absorption of ethylene gas has primarily been used only by produce harvesting and transport companies to maintain the condition of produce while it is brought to the consumer. Such ethylene gas control products have not been readily available to the consumer.
Ethylene gas contributes to the ripening process by binding to a receptor site on the plant cell membrane which causes a chemical message to be transferred to the cell nucleus in a known manner. The DNA in the nucleus begins creating RNA that eventually results in the synthesis of the enzymes which cause the particular produce to ripen and eventually spoil. It is well known to those skilled in the art that the impact of ethylene gas on the ripening process is reduced if the atmosphere surrounding the produce has a carbon dioxide concentration above approximately one percent or the surrounding atmosphere has an oxygen content below approximately eight percent. Presently, there are no consumer products that utilize atmosphere modification to control the effect of ethylene gas on produce.